Gold coatings must often have a different appearance or different physical properties for various applications. This has formerly been achieved by sputtering different gold alloys from separate targets to meet the requirements of the various applications. For example, German patent DE-C-28 25 513 teaches that the production of different gold tones by ion plating. The suggested method calls for either varying the thickness of a gold layer applied over a hard layer, or producing the topmost gold layer from a gold alloy which contains various alloying components.
This method however presents some problems. Variation of the thickness of the layer is usually impossible, because a certain thickness is necessary to make the coating of the desired durability. Variations of the composition of the topmost layer require different targets in a cathode sputtering apparatus. If coatings having two different gold standards are to be produced selectively by a cathode sputtering apparatus, for example, then two targets of different gold alloys must be on hand so as to be able to use one or the other target as required. On account of the high cost of such gold alloy targets, the result is an undesirable investment of capital in the multiple targets.
In April 1990 , printed literature of Leybold AG mentioned that gold-titanium alloys can be sputtered reactively, so that a coating of gold and titanium nitride is formed. On account of the low brilliance of the coating when alloys of low gold content are used, however, the process had been considered not very promising for decorative purposes.
The invention is addressed to the problem of developing a PVD and similar processes of the kind described above, by which different gold coatings can be applied to a substrate while minimizing expenses through the use of a single target instead of multiple targets for different coating characteristics and properties.